Generator rotor bearing preload method and apparatus

ABSTRACT

A generator has its length shortened by placing springs in a space in a casing that includes an output shaft, which is driven by an input shaft, and a yoke for separating the two shafts. The generator is assembled by placing a spring in a space in a casing having a first part. The space also has a yoke in it. A rotor bearing is placed in the space adjacent to and impinging upon the spring. A second part of the casing is attached to the first part of the casing so that the spring is pre-loaded therein. The generator also utilizes a guide for holding a spring. The generator also has a thrust plate for applying a force of the springs upon the rotor bearing.

RELATED APPLICATION

This application is a divisional application of U.S. Ser. No.12/496,713, which was filed on Jul. 2, 2009.

BACKGROUND OF THE INVENTION

Some generators, including those used with commercial aircraft, arerequired by design to disconnect from power transferred from a gearboxor other power transfer mechanism in the event of generator failure.Disconnecting the generator is a safety precaution to reduce thelikelihood that a broken generator would damage the gearbox or engineand to reduce further damage to the generator. Some generatorseffectively use a yoke having a ramp to disconnect the generator fromthe gearbox. A yoke requires axial space to disconnect a gear shaft froma generator axle.

Modern variable frequency aircraft generators typically utilize axiallypreloaded angular contact bearings in order to increase the generatorcritical speed. This preload spring has traditionally been acrest-to-crest wave spring that is placed within a generator casing.

Reduction of the weight of aircraft parts to increase the efficiency ofaircraft is a normal goal of aircraft part designers.

SUMMARY OF THE INVENTION

According to the invention, a generator has its length shortened byplacing springs in a space in a casing in which a yoke operates toseparate an output shaft from an input shaft thereby reducing the lengthand weight of the generator.

According to the invention, a method of assembling a generator involvesplacing a spring in a space in a casing having a first part. The spacealso has a yoke in it. A rotor bearing is placed adjacent to andimpinges upon the spring. Then a second part of the casing is attachedto the first part of the casing so that the spring is pre-loaded in thespace.

According to an embodiment of the invention, an aircraft generatorutilizes a spring guide for holding a spring. The spring guide has acylindrical body having an outside diameter such that a ratio of theoutside diameter of the cylindrical body to an outside diameter of thespring is approximately 0.56.

According to a further embodiment of the invention, a thrust plate foruse in an aircraft generator has a flat ring-shaped body having aninterior diameter and an exterior diameter defining a width such that aratio of the width of said body to the outer diameter is approximately0.16

According to a further embodiment of the invention, a liner for anaircraft generator having a plurality of springs therein has aring-shaped body having an inner diameter of 3.973 inches or 100.9 mmand an outer diameter of 4.337 inches or 110.16 mm, and a plurality ofcut-outs disposed in the inner diameter.

According to a still further embodiment of the invention, an assemblyfor an aircraft generator having a bearing therein has a spring guide, aspring disposed around said spring guide a liner aligning the springguide, and a thrust plate contiguous to the spring and the bearing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood by reference to thefollowing detailed description of a preferred embodiment when read inconjunction with the accompanying drawing, in which like referencecharacters refer to like parts throughout the views and in which:

FIG. 1 is a schematic cross-sectional view of a prior art generatorusing a crest-to-crest wave spring;

FIG. 2 is a perspective view of a prior art crest-to-crest wave spring;

FIG. 3 is a is a schematic cross-sectional view of a generatorincorporating the present invention;

FIG. 4 is a schematic, perspective, top view of the generatorincorporating the present invention; and

FIG. 5 is a perspective side view of a portion of the generatorincorporating the present invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE PRESENTINVENTION

Referring now to FIG. 1, a prior art embodiment of a commercial aircraftgenerator 5 having a casing 10 is shown. The generator has an inputshaft 15 that receives rotating power from a gear box (not shown) or apower source (not shown). The input shaft is selectively coupled to anoutput shaft assembly 20 that comprises an inner shaft 25 that rotateswith an outer shaft 30. The inner shaft 25 may move selectively andaxially within the outer shaft to separate the inner shaft 25 from theinput shaft 15. The outer shaft 30 supports a rotor balance assembly 35.

The rotor balance assembly 35 and the output shaft 30 are supported by apair of bearing assemblies 45. A wave spring (see also FIG. 2) 50 ispreloaded against the bearing assemblies in order to increase thegenerator critical speed as is known in the art. The wave spring isdisposed about the input shaft 15 within the casing 10.

A yoke 60 is disposed within the casing 10 at a distal end 65 of theoutput shaft assembly 20. The yoke moves towards the inner shaft 25 andengages a ramped surface 70 thereon to move the inner shaft axially awayfrom the input shaft thereby disengaging the inner shaft 25 from theinput shaft 15. In certain situations, like damage to the generator, thegenerator must be disabled to avoid damage to the gear box or otherpower source (not shown) or further damage to the generator.

The axial length of the generator 5 includes the width of the wavespring 50 (see FIG. 2). The wave spring is disposed at an end of thecasing that is distal from the yoke 60. According to the invention,however, the wave spring 50 is eliminated and axial springs 150 (as willbe described hereinbelow) are placed proximal to the yoke to eliminatethe wave spring and to thereby minimize the width of the generator 5.

Referring now to FIGS. 3-5, an embodiment of the invention is disclosed.As with the prior art, a generator 105 having a casing 110 is shown. Thegenerator has an input shaft 115 that receives rotating power from agear box (not shown) or a power source (not shown). The input shaft isselectively coupled to an output shaft assembly 120 that comprises aninner shaft 125 that rotates with an outer shaft 130. The inner shaft125 may move selectively and axially within the outer shaft to separatethe inner shaft 125 from the input shaft 115. The outer shaft 130supports a rotor balance assembly 135.

The rotor balance assembly 135 and the output shaft 130 are supported bya pair of bearing assemblies 145. A plurality of helical springs (seealso FIGS. 4 and 5) 150 are preloaded against the bearing assemblies.Each helical spring has free length of 1.645 inches or 41.783 mm and aninstalled, preloaded length of 1.305 inches or 33.147 mm. Each helicalspring is disposed upon a top-hat shaped spring guide 155 having acylinder 156 having diameter that is less than a diameter of eachhelical spring and a round base 157. Each spring guide has a length of1.060 inches or 26.924 mm such that the ratio between the length of thehelical spring and the spring guide is 1.231. Each spring has an outsidediameter of 0.575 inches or 14.605 mm and each spring guide has anoutside diameter of 0.317 inches or 8.051 mm such that the ratio of saidhelical spring diameter to the spring support diameter is 1.814. Furtherthe base 157 of the spring guide has a diameter of 0.595 inches or15.113 mm such that the ratio of the diameter of the base and theoutside diameter of the cylinder is 1.877. The spring guides minimize aprobability that the springs will buckle under load. Each cylinder 156has a pair of holes 158 to lighten the weight of the spring guides.

A flat ring-shaped thrust plate 159 engages each of the springs and abearing assembly 145. The thrust plate has an inner diameter of 2.660inches or 67.564 mm and an outer diameter of 3.925 inches or 99.695 mmdefining a width of 0.6325 inches or 16.066 mm such that a ratio betweenthe width and the outer diameter of such thrust plate is 0.161. Thethrust plate also has an outer rim 163 disposed thereon facing thebearing assembly 145.

As is known in the art, the bearing assemblies 145 need lubrication.Given the position of the thrust plate described herein, thecommunication between lubricating oil (not shown) and the bearingassemblies may be impeded. Therefore to avoid any impedance incommunication of the oil and the bearing assemblies, the thrust plate159 has a plurality of holes 161 disposed therein to allow oil to flowtherethrough.

A yoke 160 is disposed within the casing 110 in a space 162 at aproximal end 165 of the output shaft assembly 120. The yoke movestowards the inner shaft 125 and engages a ramped surface 170 thereon tomove the inner shaft axially away from the input shaft therebydisengaging the inner shaft 125 from the input shaft. In certainsituations, like damage to the generator, the generator must be disabledto avoid damage to the gear box or other power source (not shown).

Referring to FIGS. 4 and 6, the space 162 has a bearing liner 175disposed therein. The bearing liner has a ring-shaped body having aninner diameter of 3.735 inches or 94.869 mm, an outer diameter of 4.3372inches or 110.165 mm, and plurality of scalloped cutouts 180 in theinner diameter for seating the base 157 of each spring guide 155. Thespace also houses an end 185 of the yoke 160 that engages the rampedsurface 170 of the inner shaft 125. Because the end 185 is in the space162, a continuous spring could not be disposed therein. Each scallopedcutout has a radius of 0.3175 inches or 8.064 mm and encompasses an arcof 84.5 degrees. Thickness T of the liner 175 and the length of eachspring guide 156 serves to limit the compression of the helical springs150.

Referring now to FIG. 5, the assembly of the invention is shown. A firsthalf 190 of the casing 110 is disposed vertically. Each helical spring150 is disposed upon a spring guide 155. Each spring guide is placed inthe cutout 180 in the bearing liner 175 in the space 162. The thrustplate 159 is placed against each spring and the rotor balance assembly135 including the output shaft assembly 120 (See FIG. 3) is lowered ontothe thrust plate and springs in the space 162. The second half 195 (seeFIG. 3) of the casing is then attached to the first half 190 of thecasing by bolts 200. As the bolts are tightened, the helical springs 150are preloaded against a bearing assembly 145 as desired.

By switching from a wave spring 50 that is at an end of the generatorthat is distal from the yoke 60, to a plurality of helical springs 150in the essentially unused space 162 at an end of the generator that isproximal to the yoke 160, the length of the generator is reduced by thewidth of the wave spring 50. Because the yoke 160 protrudes into space162, a wave spring could not be used therein and other types of springs,like helical springs, are used.

The foregoing description is only exemplary of the principles of theinvention. Many modifications and variations are possible in light ofthe above teachings. It is, therefore, to be understood that within thescope of the appended claims, the invention may be practiced otherwisethan using the example embodiments which have been specificallydescribed. For that reason the following claims should be studied todetermine the true scope and content of this invention.

1. Method of assembling a generator having a minimized lengthcomprising: placing an axial spring in space in a casing having a firstpart, said space having a yoke therein; utilizing a spring guide toalign said spring within said space; placing a thrust plate againstspring; inserting a rotor bearing into said space such that said rotorbearing impinges upon said thrust plate; and attaching a second part ofsaid casing to said first part such that said spring is pre-loadedtherein.
 2. The method of assembling of claim 1 further comprising:placing said spring within a support before placing said spring in saidspace.
 3. The method of claim 1 wherein said spring having free lengthof approximately 41.783 mm is preloaded to an installed length of 33.147mm.
 4. A guide for a helical spring for use in an aircraft generator,said guide comprising: a cylindrical body said cylindrical body havingan outside diameter such that a ratio of the outside diameter of saidbody to an outside diameter of said spring is approximately 0.56.
 5. Theguide of claim 4 wherein said guide further comprises a round baseattached to an end of said cylindrical body wherein a ratio of thediameter of the base to said outside diameter of the cylindrical body isapproximately 1.814.
 6. A thrust plate for communicating a load on abearing in an aircraft generator, said thrust plate comprising: a flatring-shaped body having an interior diameter and an exterior diameterdefining a width such that a ratio of the width of said body to saidouter diameter is approximately 0.161.
 7. The thrust plate of claim 6wherein said thrust plate has a plurality of holes passing therethroughfor allowing a lubricating fluid to communicate through said thrustplate with said bearing.
 8. The thrust plate of claim 6 in which saidring-shaped body has a rim disposed along its outer diameter.
 9. A linerfor a generator having a plurality of springs therein comprising: aring-shaped body having an inner diameter of 94.869 mm and an outerdiameter of approximately 4.334 inches; and a cut-out disposed in saidinner diameter therein, said cutout supporting a spring.
 10. The linerof claim 9 wherein each cut-out defines an arc of approximately 84.5degrees.
 11. The liner of claim 10 wherein each cut-out defines a radiusof approximately 8.064 mm.
 12. An assembly for an aircraft generatorhaving a bearing therein comprising: a spring guide; a spring disposedaround said spring guide; a liner aligning said spring guide; and athrust plate contiguous to said spring and the bearing.
 13. The assemblyof claim 12 wherein a ratio of an installed length of said spring and alength of said spring guide is approximately 1.231 to one.
 14. Theassembly of claim 12 wherein said thrust plate has a flat ring-shapedbody having an interior diameter and an exterior diameter defining awidth such that a ratio of the width of said body to said outer diameteris approximately 0.161.
 15. The assembly of claim 12 wherein said linercomprises a ring-shaped body having a plurality of cut-outs disposed insaid inner diameter therein
 16. The assembly of claim 15 wherein eachcut-out defines an arc of approximately 84.5 degrees.
 17. The assemblyof claim 13 wherein said spring guide comprises: a cylindrical body saidcylindrical body having an outside diameter such that a ratio of theoutside diameter of said spring to an outside diameter of said body isapproximately 0.56.
 18. The assembly of claim 13 wherein said guidefurther comprises a round base attached to an end of said cylindricalbody wherein a ratio of the diameter of the base to said outsidediameter of the cylindrical body is approximately 1.877.